Prevalence of cross-reactive HIV-1-neutralizing activity in HIV-1-infected patients with rapid or slow disease progression

Functional and Molecular Characteristics of Novel and Conserved Cross-Clade HIV Envelope Specific Human Monoclonal Antibodies

To define features of the B cell response to HIV that may be translated to vaccine development, we have isolated a panel of monoclonal antibodies (MAbs) from HIV-infected patients. These MAbs are all highly reactive to HIV envelope (Env) from multiple clades, and include gp120 and gp41 specificities. Three of the MAbs exhibit substantial homology to previously described VH1-69, VH3-30, and VH4-59 HIV broadly neutralizing antibody lineages. An inherently autoreactive VH4-34 encoded MAb was reactive to diverse Env despite its minimal mutation from germline. Its isolation is consistent with our previous observation of increased VH4-34+antibodies in HIV-infected patients. These results suggest that conserved developmental processes contribute to immunoglobulin repertoire usage and maturation in response to HIV Env and that intrinsically autoreactive VH genes, despite the absence of mutation, could serve as effective templates for maturation and development of protective antibodies. These results also bear significant implications for the development of immunogens.

Broadly Neutralizing Antibody Responses in a Large Longitudinal Sub-Saharan HIV Primary Infection Cohort

Broadly neutralizing antibodies (bnAbs) are thought to be a critical component of a protective HIV vaccine. However, designing vaccines immunogens able to elicit bnAbs has proven unsuccessful to date. Understanding the correlates and immunological mechanisms leading to the development of bnAb responses during natural HIV infection is thus critical to the design of a protective vaccine. The IAVI Protocol C program investigates a large longitudinal cohort of primary HIV-1 infection in Eastern and South Africa. Development of neutralization was evaluated in 439 donors using a 6 cross-clade pseudo-virus panel predictive of neutralization breadth on larger panels. About 15% of individuals developed bnAb responses, essentially between year 2 and year 4 of infection. Statistical analyses revealed no influence of gender, age or geographical origin on the development of neutralization breadth. However, cross-clade neutralization strongly correlated with high viral load as well as with low CD4 T cell counts, subtype-C infection and HLA-A*03(-) genotype. A correlation with high overall plasma IgG levels and anti-Env IgG binding titers was also found. The latter appeared not associated with higher affinity, suggesting a greater diversity of the anti-Env responses in broad neutralizers. Broadly neutralizing activity targeting glycan-dependent epitopes, largely the N332-glycan epitope region, was detected in nearly half of the broad neutralizers while CD4bs and gp41-MPER bnAb responses were only detected in very few individuals. Together the findings suggest that both viral and host factors are critical for the development of bnAbs and that the HIV Env N332-glycan supersite may be a favorable target for vaccine design.

Viral vaccines and their manufacturing cell substrates: New trends and designs in modern vaccinology

Vaccination is one of the most effective interventions in global health. The worldwide vaccination programs significantly reduced the number of deaths caused by infectious agents. A successful example was the eradication of smallpox in 1979 after two centuries of vaccination campaigns. Since the first variolation administrations until today, the knowledge on immunology has increased substantially. This knowledge combined with the introduction of cell culture and DNA recombinant technologies revolutionized vaccine design. This review will focus on vaccines against human viral pathogens, recent developments on vaccine design and cell substrates used for their manufacture. While the production of attenuated and inactivated vaccines requires the use of the respective permissible cell substrates, the production of recombinant antigens, virus‐like particles, vectored vaccines and chimeric vaccines requires the use – and often the development – of specific cell lines. Indeed, the development of novel modern viral vaccine designs combined with, the stringent safety requirements for manufacture, and the better understanding on animal cell metabolism and physiology are increasing the awareness on the importance of cell line development and engineering areas. A new era of modern vaccinology is arriving, offering an extensive toolbox to materialize novel and creative ideas in vaccine design and its manufacture.

Immunogens Modeling a Fusion-Intermediate Conformation of gp41 Elicit Antibodies to the Membrane Proximal External Region of the HIV Envelope Glycoprotein

The membrane proximal external region (MPER) of the gp41 subunit of the HIV-1 envelope glycoprotein (Env) contains determinants for broadly neutralizing antibodies and has remained an important focus of vaccine design. However, creating an immunogen that elicits broadly neutralizing antibodies to this region has proven difficult in part due to the relative inaccessibility of the MPER in the native conformation of Env. Here, we describe the antigenicity and immunogenicity of a panel of oligomeric gp41 immunogens designed to model a fusion-intermediate conformation of Env in order to enhance MPER exposure in a relevant conformation. The immunogens contain segments of the gp41 N- and C-heptad repeats to mimic a trapped intermediate, followed by the MPER, with variations that include different N-heptad lengths, insertion of extra epitopes, and varying C-termini. These well-characterized immunogens were evaluated in two different immunization protocols involving gp41 and gp140 proteins, gp41 and gp160 DNA primes, and different immunization schedules and adjuvants. We found that the immunogens designed to reduce extension of helical structure into the MPER elicited the highest MPER antibody binding titers, but these antibodies lacked neutralizing activity. The gp41 protein immunogens also elicited higher MPER titers than the gp140 protein immunogen. In prime-boost studies, the best MPER responses were seen in the groups that received DNA priming with gp41 vectors followed by gp41 protein boosts. Finally, although titers to the entire protein immunogen were similar in the two immunization protocols, MPER-specific titers differed, suggesting that the immunization route, schedule, dose, or adjuvant may differentially influence MPER immunogenicity. These findings inform the design of future MPER immunogens and immunization protocols.

An investigation of the breadth of neutralizing antibody response in cats naturally infected with feline immunodeficiency virus

Neutralizing antibodies (NAbs) are believed to comprise an essential component of the protective immune response induced by vaccines against feline immunodeficiency virus (FIV) and human immunodeficiency virus (HIV) infections. However, relatively little is known about the role of NAbs in controlling FIV infection and subsequent disease progression. Here, we present studies where we examined the neutralization of HIV-luciferase pseudotypes bearing homologous and heterologous FIV envelope proteins (n = 278) by sequential plasma samples collected at 6 month intervals from naturally infected cats (n = 38) over a period of 18 months. We evaluated the breadth of the NAb response against non-recombinant homologous and heterologous clade A and clade B viral variants, as well as recombinants, and assessed the results, testing for evidence of an association between the potency of the NAb response and the duration of infection, CD4⁺ T lymphocyte numbers, health status and survival times of the infected cats. Neutralization profiles varied significantly between FIV-infected cats and strong autologous neutralization, assessed using luciferase-based in vitro assays, did not correlate with the clinical outcome. No association was observed between strong NAb responses and either improved health status or increased survival time of infected animals, implying that other protective mechanisms were likely to be involved. Similarly, no correlation was observed between the development of autologous NAbs and the duration of infection. Furthermore, cross-neutralizing antibodies were evident in only a small proportion (13 %) of cats.

How does the humoral response to HIV-2 infection differ from HIV-1 and can this explain the distinct natural history of infection with these two human retroviruses?

A substantial proportion of people infected with HIV-2, the second causative agent of acquired immune deficiency syndrome (AIDS), behave as long-term non-progressors (LTNP) and are able to control the infection more effectively than most HIV-1-infected patients. A better understanding of the differences in the natural history of HIV-1 and HIV-2 infection, and how these relate to the relative immunogenicity and evolution of the two virus strains, could provide important insights into the mechanisms of protective immunity in HIV infection. One of the most striking differences is that most people infected with HIV-2 generate high titers of broadly neutralizing antibodies, whereas this is relatively uncommon in HIV-1 infection. In this review we compare the underlying structural differences of the envelope (Env) between HIV-1 and HIV-2, and examine how these might affect the antibody responses as well as their impact on Env evolution and control of viral replication.

Early preservation of CXCR5+ PD-1+ helper T cells and B cell activation predict the breadth of neutralizing antibody responses in chronic HIV-1 infection

Much is known about the characteristics of broadly neutralizing antibodies (bNAbs) generated during HIV-1 infection, but little is known about immunological mechanisms responsible for their development in only a minority of those infected by HIV-1. By monitoring longitudinally a cohort of HIV-1-infected subjects, we observed that the preservation of CXCR5(+) CD4(+) T helper cell frequencies and activation status of B cells during the first year of infection correlates with the maximum breadth of plasma neutralizing antibody responses during chronic infection independently of viral load. Although, during the first year of infection, no differences were observed in the abilities of peripheral CXCR5(+) CD4(+) T helper cells to induce antibody secretion by autologous naive B cells, higher frequencies of class-switched antibodies were detected in cocultures of CXCR5(+) CD4(+) T and B cells from the subjects who later developed broadly neutralizing antibody responses than those who did not. Furthermore, B cells from the former subjects had higher expression of AICDA than B cells from the latter subjects, and transcript levels correlated with the frequency of CXCR5(+) CD4(+) T cells. Thus, the early preservation of CXCR5(+) CD4(+) T cells and B cell function are central to the development of bNAbs. Our study provides a possible explanation for their infrequent generation during HIV-1 infection.

IMPORTANCE

Broadly neutralizing antibodies are developed by HIV-1-infected subjects, but so far (and despite intensive efforts over the past 3 decades) they have not been elicited by immunization. Understanding how bNAbs are generated during natural HIV-1 infection and why only some HIV-1-infected subjects generate such antibodies will assist our efforts to elicit bNAbs by immunization. CXCR5(+) PD-1(+) CD4(+) T cells are critical for the development of high-affinity antigen-specific antibody responses. In our study, we found that the HIV-1-infected subjects who develop bNAbs have a higher frequency of peripheral CXCR5(+) PD-1(+) CD4(+) T cells in early infection and also that this frequency mirrored what was observed in uninfected subjects and correlated with the level of B cell activation across subjects. Our study highlights the critical role helper T cell function has in the elicitation of broadly neutralizing antibody responses in the context of HIV infection.

Immunogen design for HIV-1 and influenza

Vaccines provide the most cost effective defense against pathogens. Although vaccines have been designed for a number of viral diseases, a vaccine against HIV-1 still remains elusive. In contrast, while there are excellent influenza vaccines, these need to be changed every few years because of antigenic drift and shift. The recent discovery of a large number of broadly neutralizing antibodies (bNAbs) and structural characterization of the conserved epitopes targeted by them presents an opportunity for structure based HIV-1 and influenza A vaccine design. We discuss strategies to design immunogens either targeting a particular antigenic region or focusing on native structure stabilization. This article is part of a Special Issue entitled: Recent advances in molecular engineering of antibody.

Early development of broadly neutralizing antibodies in HIV-1-infected infants

Eliciting protective neutralizing antibodies (NAbs) against HIV-1 is daunting because of the extensive genetic and antigenic diversity of HIV-1. Moreover, broad and potent responses are uncommon even during persistent infection, with only a subset of adults developing broadly neutralizing antibodies (bNAbs) that recognize variants from different HIV-1 clades^1–8. It is not known whether bNAbs can also arise in HIV-1-infected infants, who typically progress to disease faster than adults⁹, presumably in part due to an immature immune system¹⁰. Here, we show that bNAbs develop at least as commonly in infants as in adults. Cross-clade NAb responses were detected in 20/28 infected infants, in some cases, within 1 year of infection. Among infants with the top quartile of responses, neutralization of Tier 2–3 variants from multiple clades was detected at 20 months post-infection. These findings suggest that, even in early life, there is sufficient B-cell functionality to mount bNAbs against HIV-1. Additionally, the relatively early appearance of bNAbs in infants may provide a unique setting for understanding the pathways of B-cell maturation leading to bNAbs.

Early development of broadly reactive HIV-1 neutralizing activity in elite neutralizers

Broadly reactive neutralizing activity (brNA) against HIV-1 is observed in 10-30% of infected individuals and generally takes 2-4 years to develop. Here, we show that two elite neutralizers, infected through injecting drug use, developed brNA around the first year postseroconversion (post-SC), whereas criteria for elite brNA were fulfilled around 30 months post-SC. These results indicate that brNA does not necessarily require multiple years to develop and they should encourage the search for vaccines that can elicit protective humoral immunity.

HIV-1 specific antibody titers and neutralization among chronically infected patients on long-term suppressive antiretroviral therapy (ART): a cross-sectional study

The majority of potent and broadly neutralizing antibodies against HIV-1 have been isolated from untreated patients with acute or chronic infection. To assess the extent of HIV-1 specific antibody response and neutralization after many years of virologic suppression from potent combination ART, we examined antibody binding titers and neutralization of 51 patients with chronic HIV-1 infection on suppressive ART for at least three years. In this cross-sectional analysis, we found high antibody titers against gp120, gp41, and the membrane proximal external region (MPER) in 59%, 43%, and 27% of patients, respectively. We observed significantly higher endpoint binding titers for gp120 and gp41 for patients with >10 compared to ≤10 years of detectable HIV RNA. Additionally, we observed higher median gp120 and gp41 antibody titers in patients with HIV RNA <50 copies/mL for ≤5 years. 22% of patients neutralized a HIV-1 primary isolate (HIV-1_JR-FL) and 8% neutralized a HIV-2/HIV-1 MPER chimera. Significantly greater HIV-1_JR-FL neutralization was found among patients with >10 years of detectable HIV RNA (8/20 [40.0%] versus 3/31 [9.7%] for ≤10 years, p = 0.02) and a trend toward greater neutralization in patients with ≤5 years of HIV RNA <50 copies/mL (7/20 [35.0%] versus 4/31 [12.9%] for >5 years, p = 0.08). All patients with neutralizing activity mediated successful phagocytosis of VLPs by THP-1 cells after antibody opsonization. Our findings of highly specific antibodies to several structural epitopes of HIV-1 with antibody effector functions and neutralizing activity after long-term suppressive ART, suggest continuous antigenic stimulation and evolution of HIV-specific antibody response occurs before and after suppression with ART. These patients, particularly those with slower HIV progression and more time with detectable viremia prior to initiation of suppressive ART, are a promising population to identify and further study functional antibodies against HIV-1.

Diverse recombinant HIV-1 Envs fail to activate B cells expressing the germline B cell receptors of the broadly neutralizing anti-HIV-1 antibodies PG9 and 447-52D

Broadly neutralizing antibodies (bNAbs) against HIV-1 are generated during HIV-1-infection but have not yet been elicited by immunization with recombinant forms of the viral envelope glycoprotein (Env; the target of anti-HIV-1 neutralizing antibodies). A particular type of bNAb targets the CD4-binding site (CD4-BS) region of Env. These antibodies are derived from a limited number of VH/VL genes and can bind to and neutralize diverse HIV-1 strains. Recent reports have demonstrated the limited potential of Env to activate B cells expressing the germline B cell receptor (BCR) forms of anti-CD4-BS bNAbs. A potential reason for the lack of elicitation of anti-CD4-BS bNAbs by Env immunogens is the absence of stimulation of naive B cells expressing the germline BCRs of such antibodies. Several bNAbs have been isolated from HIV-1-infected subjects that target other structurally conserved regions of Env. How frequently Env immunogens stimulate the germline BCRs that give rise to bNAbs that target Env regions other than the CD4-BS is not well understood. Here, we investigated the interactions between diverse Envs and the BCRs of known bNAbs targeting not only the CD4-BS but also conserved elements of the second and third variable Env regions. Our results indicate that Env is generally ineffective in engaging germline BCRs of bNAbs irrespective of their epitope target. Potentially, this is the result of viral evolutionary mechanisms adopted to escape broadly neutralizing antibody responses. Our results also suggest that a single Env capable of activating germline BCRs that target distinct Env epitopes will be very difficult to identify or to design.

IMPORTANCE

Broadly neutralizing antibodies against HIV-1 are thought to be an important component of the immune responses that a successful vaccine should elicit. Broadly neutralizing antibodies are generated by a subset of those infected by HIV-1, but so far, they have not been generated by immunization with recombinant Envelope (Env, the target of anti-HIV-1 neutralizing antibodies). Here, we provide evidence that the inability of Env to elicit the production of broadly neutralizing antibodies is due to the inability of diverse Envs to engage the germline B cell receptor forms of known broadly neutralizing antibodies.

HIV-1 envelope glycoprotein signatures that correlate with the development of cross-reactive neutralizing activity

BACKGROUND

Current HIV-1 envelope glycoprotein (Env) vaccines are unable to induce cross-reactive neutralizing antibodies. However, such antibodies are elicited in 10-30% of HIV-1 infected individuals, but it is unknown why these antibodies are induced in some individuals and not in others. We hypothesized that the Envs of early HIV-1 variants in individuals who develop cross-reactive neutralizing activity (CrNA) might have unique characteristics that support the induction of CrNA.

RESULTS

We retrospectively generated and analyzed env sequences of early HIV-1 clonal variants from 31 individuals with diverse levels of CrNA 2-4 years post-seroconversion. These sequences revealed a number of Env signatures that coincided with CrNA development. These included a statistically shorter variable region 1 and a lower probability of glycosylation as implied by a high ratio of NXS versus NXT glycosylation motifs. Furthermore, lower probability of glycosylation at position 332, which is involved in the epitopes of many broadly reactive neutralizing antibodies, was associated with the induction of CrNA. Finally, Sequence Harmony identified a number of amino acid changes associated with the development of CrNA. These residues mapped to various Env subdomains, but in particular to the first and fourth variable region as well as the underlying α2 helix of the third constant region.

CONCLUSIONS

These findings imply that the development of CrNA might depend on specific characteristics of early Env. Env signatures that correlate with the induction of CrNA might be relevant for the design of effective HIV-1 vaccines.

A Blueprint for HIV Vaccine Discovery

Despite numerous attempts over many years to develop an HIV vaccine based on classical strategies, none has convincingly succeeded to date. A number of approaches are being pursued in the field, including building upon possible efficacy indicated by the recent RV144 clinical trial, which combined two HIV vaccines. Here, we argue for an approach based, in part, on understanding the HIV envelope spike and its interaction with broadly neutralizing antibodies (bnAbs) at the molecular level and using this understanding to design immunogens as possible vaccines. BnAbs can protect against virus challenge in animal models, and many such antibodies have been isolated recently. We further propose that studies focused on how best to provide T cell help to B cells that produce bnAbs are crucial for optimal immunization strategies. The synthesis of rational immunogen design and immunization strategies, together with iterative improvements, offers great promise for advancing toward an HIV vaccine.

Specific antibody-dependent cellular cytotoxicity responses associated with slow progression of HIV infection

Antibody-dependent cellular cytotoxicity (ADCC) is potentially an effective adaptive immune response to HIV infection. However, little is understood about the role of ADCC in controlling chronic infection in the small number of long-term slow-progressors (LTSP) who maintain a relatively normal immunological state for prolonged periods of time. We analysed HIV-specific ADCC responses in sera from 139 HIV(+) subjects not on antiretroviral therapy. Sixty-five subjects were LTSP, who maintained a CD4 T-cell count > 500/μl for over 8 years after infection without antiretroviral therapy and 74 were non-LTSP individuals. The ADCC responses were measured using an natural killer cell activation assay to overlapping HIV peptides that allowed us to map ADCC epitopes. We found that although the magnitude of ADCC responses in the LTSP cohort were not higher and did not correlate with CD4 T-cell depletion rates, the LTSP cohort had significantly broader ADCC responses compared with the non-LTSP cohort. Specifically, regulatory/accessory HIV-1 proteins were targeted more frequently by LTSP. Indeed, three particular ADCC epitopes within the Vpu protein of HIV were recognized only by LTSP individuals. Our study provides evidence that broader ADCC responses may play a role in long-term control of HIV progression and suggests novel vaccine targets.

Short communication: neutralizing antibodies in HIV-1-infected Brazilian individuals

Tests for the detection of the humoral immune response to HIV-1 have to be standardized and established, demanding regional efforts. For this purpose the neutralizing antibody (NAb) assay for HIV-1 in TZM-bl cells was introduced in Brazil. Twenty plasma samples from HIV-1-infected individuals were assayed: 10 progressors and 10 long-term nonprogressors. These were tested against eight env-pseudotyped viruses (psVs) in the TZM-bl NAb assay and against HIV-1 strain HTLV/IIIB (HIV-1 IIIB) in primary lymphocytes. Forty-four percent of the samples showed neutralizing titers for psVs and 55% for HIV-1 IIIB. Plasma from progressors showed a broader neutralization and a higher potency. The introduction of these reference reagents encourages the participation of Brazil in future comparative assessments of anti-HIV-1 antibodies.

Expansion of antibody secreting cells and modulation of neutralizing antibody activity in HIV infected individuals undergoing structured treatment interruptions

Background

HIV-1 infection generates numerous abnormalities in the B cell compartment which can be partly reversed by antiretroviral therapy. Our aim was to evaluate the effects that re-exposure to HIV antigens might have on the frequency and functionality of antibody secreting cells (ASC) in patients undergoing structured treatment interruptions (STI). As re-exposure to viral antigens may also boost the production of (neutralizing) antibodies, we also assessed the neutralizing activities during STI cycles.

Methods

Retrospective study of 10 patients undergoing 3 cycles of STI with 2 weeks on and 4 weeks off HAART. ASC frequencies were determined by flow cytometry in samples obtained at the beginning and the end of STI. Neutralization capacity, total IgG concentration and anti-gp120-IgG titres were evaluated.

Results

As expected, median viral loads were higher at the end of STI compared to on-HAART time points. The level of CD27 and CD38 expressing ACS followed the same pattern; with ASC being elevated up to 16 fold in some patients (median increase of 3.5% ± 4.13). Eight out of 10 patients maintained stable total IgG levels during the study. After purifying IgG fractions from plasma, HIV-neutralizing activity was observed in the two subjects with highest anti-gp120 titers. In one of these patients the neutralizing activity remained constant while the other showed elevated neutralizing Ab after first STI and once treatment was reinitiated after the 2^nd STI.

Conclusions

Our data suggest that STI and its associated transient increases in viral load drive the frequencies of ASC in an antigen-specific manner. In some subjects, this re-exposure to autologous virus boosts the presence of neutralizing antibodies, similar to what is seen after influenza vaccination. STI may not boost clinically beneficial nAb levels but offers opportunities to isolate nAb producing cells at considerably higher levels than in subjects with completely suppressed viral replication.

Broadly neutralizing antibodies against HIV-1: templates for a vaccine

The need for an effective vaccine to prevent the global spread of human immunodeficiency virus type 1 (HIV-1) is well recognized. Passive immunization and challenge studies in non-human primates testify that broadly neutralizing antibodies (BrNAbs) can accomplish protection against infection. In recent years, the introduction of new techniques has facilitated the discovery of an unprecedented number of new human BrNAbs that target and delineate diverse conserved epitopes on the envelope glycoprotein spike (Env). The epitopes of these BrNAbs can serve as templates for immunogen design aimed to induce similar antibodies. Here we will review the characteristics of the different classes of BrNAbs and their target epitopes, as well as factors associated with their development and implications for vaccine design.

Genome-wide association study on the development of cross-reactive neutralizing antibodies in HIV-1 infected individuals

Broadly neutralizing antibodies may protect against HIV-1 acquisition. In natural infection, only 10–30% of patients have cross-reactive neutralizing humoral immunity which may relate to viral and or host factors. To explore the role of host genetic markers in the formation of cross-reactive neutralizing activity (CrNA) in HIV-1 infected individuals, we performed a genome-wide association study (GWAS), in participants of the Amsterdam Cohort Studies with known CrNA in their sera. Single-nucleotide polymorphisms (SNPs) with the strongest P-values are located in the major histocompatibility complex (MHC) region, close to MICA (P = 7.68×10⁻⁷), HLA-B (P = 6.96×10⁻⁶) and in the coding region of HCP5 (P = 1.34×10⁻⁵). However, none of the signals reached genome-wide significance. Our findings underline the potential involvement of genes close or within the MHC region with the development of CrNA.

Neutralization sensitivity of HIV-1 subtype B' clinical isolates from former plasma donors in China

BACKGROUND

HIV-1 subtype B' isolates have been predominantly circulating in China. Their intra- and inter-subtype neutralization sensitivity to autologous and heterologous plasmas has not been well studied.

RESULTS

Twelve HIV-1 B' clinical isolates obtained from patients were tested for their intra- and inter-subtype neutralization sensitivity to the neutralization antibodies in the plasmas from patients infected by HIV-1 B' and CRF07_BC subtypes, respectively. We found that the plasmas from the HIV-1 B'-infected patients could potently neutralize heterologous viruses of subtype B' with mean ID50 titer (1/x) of about 67, but they were not effective in neutralizing autologous viruses of subtype B' with mean ID50 titer (1/x) of about 8. The plasmas from HIV-1 CRF07_BC-infected patients exhibited weak inter-subtype neutralization activity against subtype B' viruses with ID50 titer (1/x) is about 22. The neutralization sensitivity of HIV-1 B' isolates was inversely correlated with the neutralizing activity of plasmas from HIV-1 B'-infected patients (Spearman's r = -0.657, P = 0.020), and with the number of potential N-glycosylation site (PNGS) in V1-V5 region (Spearman's r = -0.493, P = 0.034), but positively correlated with the viral load (Spearman's r = 0.629, P = 0.028). It had no correlation with the length of V1-V5 regions or the CD4+ T cell count. Virus AH259V has low intra-subtype neutralization sensitivity, it can be neutralized by 17b (IC50: 10μg/ml) and 447-52D (IC50: 1.6μg/ml), and the neutralizing antibodies (nAbs) in plasma AH259P are effective in neutralizing infection by the primary HIV-1 isolates with different subtypes with ID50 titers (1/x) in the range of 32-396.

CONCLUSIONS

These findings suggest that the HIV-1 subtype B' viruses may mutate under the immune pressure, thus becoming resistant to the autologous nAbs, possibly by changing the number of PNGS in the V1-V5 region of the viral gp120. Some of primary HIV-1 isolates are able to induce both intra- and inter-subtype cross-neutralizing antibody responses.

Resistance to antibody neutralization in HIV-2 infection occurs in late stage disease and is associated with X4 tropism

OBJECTIVES

To characterize the nature and dynamics of the neutralizing antibody (NAb) response and escape in chronically HIV-2 infected patients.

METHODS

Twenty-eight chronically infected adults were studied over a period of 1-4 years. The neutralizing activity of plasma immunoglobulin G (IgG) antibodies against autologous and heterologous primary isolates was analyzed using a standard assay in TZM-bl cells. Coreceptor usage was determined in ghost cells. The sequence and predicted three-dimensional structure of the C2V3C3 Env region were determined for all isolates.

RESULTS

Only 50% of the patients consistently produced IgG NAbs to autologous and contemporaneous virus isolates. In contrast, 96% of the patients produced IgG antibodies that neutralized at least two isolates of a panel of six heterologous R5 isolates. Breadth and potency of the neutralizing antibodies were positively associated with the number of CD4(+) T cells and with the titer and avidity of C2V3C3-specific binding IgG antibodies. X4 isolates were obtained only from late stage disease patients and were fully resistant to neutralization. The V3 loop of X4 viruses was longer, had a higher net charge, and differed markedly in secondary structure compared to R5 viruses.

CONCLUSION

Most HIV-2 patients infected with R5 isolates produce C2V3C3-specific neutralizing antibodies whose potency and breadth decreases as the disease progresses. Resistance to antibody neutralization occurs in late stage disease and is usually associated with X4 viral tropism and major changes in V3 sequence and conformation. Our studies support a model of HIV-2 pathogenesis in which the neutralizing antibodies play a central role and have clear implications for the vaccine field.

Evolution of cross-neutralizing antibody specificities to the CD4-BS and the carbohydrate cloak of the HIV Env in an HIV-1-infected subject

Broadly neutralizing antibodies are considered an important part of a successful HIV vaccine. A better understanding of the factors underlying their development during infection and of the epitopes they target is needed to elicit similar antibody responses by vaccination. We and others reported that, on average, it takes 2 to 3 years for cross-reactive neutralizing antibodies to become detectable in the sera of HIV-1-infected subjects and that they target a limited number of epitopes on the HIV Envelope. Here we investigated the emergence and evolution of the earliest cross-reactive neutralizing antibody specificities in one HIV-1-infected individual, AC053. We defined two distinct epitopes on Env that are targeted by the broadly neutralizing antibody responses developed by AC053. The first specificity became evident at 3 years post infection and targeted the CD4-binding site of Env. Antibodies responsible for that specificity neutralized most, but not all, viruses susceptible to neutralization by the plasma antibodies of AC053. The second specificity became apparent approximately a year later. It was due to PG9-like antibodies, which were able to neutralize those viruses not susceptible to the anti-CD4-BS antibodies in AC053. These findings improve our understanding of the co-development of broadly neutralizing antibodies that target more than one epitope during natural HIV-1-infection in selected HIV+ subjects. They support the hypothesis that developing broadly neutralizing antibody responses targeting distinct epitopes by immunization could be feasible.

Human immunodeficiency virus type-1 (HIV-1) continues to evolve in presence of broadly neutralizing antibodies more than ten years after infection

Background

The evolution of HIV-1 and its immune escape to autologous neutralizing antibodies (Nabs) during the acute/early phases of infection have been analyzed in depth in many studies. In contrast, little is known about neither the long-term evolution of the virus in patients who developed broadly Nabs (bNabs) or the mechanism of escape in presence of these bNabs.

Results

We have studied the viral population infecting a long term non progressor HIV-1 infected patient who had developed broadly neutralizing antibodies toward all tier 2/3 viruses (6 clades) tested, 9 years after infection, and was then followed up over 7 years. The autologous neutralization titers of the sequential sera toward env variants representative of the viral population significantly increased during the follow-up period. The most resistant pseudotyped virus was identified at the last visit suggesting that it represented a late emerging escape variant. We identified 5 amino acids substitutions that appeared associated with escape to broadly neutralizing antibodies. They were V319I/S, R/K355T, R/W429G, Q460E and G/T463E, in V3, C3 and V5 regions.

Conclusion

This study showed that HIV-1 may continue to evolve in presence of both broadly neutralizing antibodies and increasing autologous neutralizing activity more than 10 years post-infection.

B-lymphocyte dysfunction in chronic HIV-1 infection does not prevent cross-clade neutralization breadth

Aberrant expression of regulatory receptors programmed death-1 (PD-1) and B- and T-lymphocyte attenuator (BTLA) is linked with dysregulation and exhaustion of T lymphocytes during chronic human immunodeficiency virus type 1 (HIV-1) infection; however, less is known about whether a similar process impacts B-lymphocyte function during HIV-1 infection. We reasoned that disruption of the peripheral B cell compartment might be associated with decreased neutralizing antibody activity. Expression of markers that indicate dysregulation (BTLA and PD-1), immune activation (CD95), and proliferation (Ki-67) was evaluated in B cells from HIV-1-infected viremic and aviremic subjects and healthy subjects, in conjunction with immunoglobulin production and CD4 T cell count. Viral load and cross-clade neutralizing activity in plasma from viremic subjects were also assessed. Dysregulation of B lymphocytes was indicated by a marked disruption of peripheral B cell subsets, increased levels of PD-1 expression, and decreased levels of BTLA expression in viremic subjects compared to aviremic subjects and healthy controls. PD-1 and BTLA were correlated in a divergent fashion with immune activation, CD4 T cell count, and the total plasma IgG level, a functional correlate of B cell dysfunction. Within viremic subjects, the total IgG level correlated directly with cross-clade neutralizing activity in plasma. The findings demonstrate that even in chronically infected subjects in which B lymphocytes display multiple indications of dysfunction, antibodies that mediate cross-clade neutralization breadth continue to circulate in plasma.

Cross-reactive broadly neutralizing antibodies: timing is everything

The recent surge of research into new broadly neutralizing antibodies in HIV-1 infection has recharged the field of HIV-1 vaccinology. In this review we discuss the currently known broadly neutralizing antibodies and focus on factors that may shape these antibodies in natural infection. We further discuss the role of these antibodies in the clinical course of the infection and consider immunological obstacles in inducing broadly neutralizing antibodies with a vaccine.

9G4 autoreactivity is increased in HIV-infected patients and correlates with HIV broadly neutralizing serum activity

The induction of a broadly neutralizing antibody (BNAb) response against HIV-1 would be a desirable feature of a protective vaccine. Vaccine strategies thus far have failed to elicit broadly neutralizing antibody responses; however a minority of HIV-infected patients do develop circulating BNAbs, from which several potent broadly neutralizing monoclonal antibodies (mAbs) have been isolated. The findings that several BNmAbs exhibit autoreactivity and that autoreactive serum antibodies are observed in some HIV patients have advanced the possibility that enforcement of self-tolerance may contribute to the rarity of BNAbs. To examine the possible breakdown of tolerance in HIV patients, we utilized the 9G4 anti-idiotype antibody system, enabling resolution of both autoreactive VH4-34 gene-expressing B cells and serum antibodies. Compared with healthy controls, HIV patients had significantly elevated 9G4+ serum IgG antibody concentrations and frequencies of 9G4+ B cells, a finding characteristic of systemic lupus erythematosus (SLE) patients, both of which positively correlated with HIV viral load. Compared to the global 9G4-IgD--memory B cell population, the 9G4+IgD--memory fraction in HIV patients was dominated by isotype switched IgG+ B cells, but had a more prominent bias toward "IgM only" memory. HIV envelope reactivity was observed both in the 9G4+ serum antibody and 9G4+ B cell population. 9G4+ IgG serum antibody levels positively correlated (r = 0.403, p = 0.0019) with the serum HIV BNAbs. Interestingly, other serum autoantibodies commonly found in SLE (anti-dsDNA, ANA, anti-CL) did not correlate with serum HIV BNAbs. 9G4-associated autoreactivity is preferentially expanded in chronic HIV infection as compared to other SLE autoreactivities. Therefore, the 9G4 system provides an effective tool to examine autoreactivity in HIV patients. Our results suggest that the development of HIV BNAbs is not merely a consequence of a general breakdown in tolerance, but rather a more intricate expansion of selective autoreactive B cells and antibodies.

Targeting HIV-1 envelope glycoprotein trimers to B cells by using APRIL improves antibody responses

An HIV-1 vaccine remains elusive, in part because various factors limit the quantity and quality of the antibodies raised against the viral envelope glycoprotein complex (Env). We hypothesized that targeting Env vaccines directly to B cells, by fusing them to molecules that bind and activate these cells, would improve Env-specific antibody responses. Therefore, we fused trimeric Env gp140 to A PRoliferation-Inducing Ligand (APRIL), B-cell Activating Factor (BAFF), and CD40 Ligand (CD40L). The Env-APRIL, Env-BAFF, and Env-CD40L gp140 trimers all enhanced the expression of activation-induced cytidine deaminase (AID), the enzyme responsible for inducing somatic hypermutation, antibody affinity maturation, and antibody class switching. They also triggered IgM, IgG, and IgA secretion from human B cells in vitro. The Env-APRIL trimers induced higher anti-Env antibody responses in rabbits, including neutralizing antibodies against tier 1 viruses. The enhanced Env-specific responses were not associated with a general increase in total plasma antibody concentrations, indicating that the effect of APRIL was specific for Env. All the rabbit sera raised against gp140 trimers, irrespective of the presence of CD40L, BAFF, or APRIL, recognized trimeric Env efficiently, whereas sera raised against gp120 monomers did not. The levels of trimer-binding and virus-neutralizing antibodies were strongly correlated, suggesting that gp140 trimers are superior to gp120 monomers as immunogens. Targeting and activating B cells with a trimeric HIV-1 Env-APRIL fusion protein may therefore improve the induction of humoral immunity against HIV-1.

Longitudinal analysis of early HIV-1-specific neutralizing activity in an elite neutralizer and in five patients who developed cross-reactive neutralizing activity

We previously established that at 3 years postseroconversion, ~30% of HIV-infected individuals have cross-reactive neutralizing activity (CrNA) in their sera. Here we studied the kinetics with which CrNA develops and how these relate to the development of autologous neutralizing activity as well as viral escape and diversification. For this purpose, sera from five individuals with CrNA and one elite neutralizer that were obtained at three monthly intervals in the first year after seroconversion and at multiple intervals over the disease course were tested for neutralizing activity against an established multiclade panel of six viruses. The same serum samples, as well as sera from three individuals who lacked CrNA, were tested for their neutralizing activities against autologous clonal HIV-1 variants from multiple time points covering the disease course from seroconversion onward. The elite neutralizer already had CrNA at 9.8 months postseroconversion, in contrast with the findings for the other five patients, in whom CrNA was first detected at 20 to 35 months postseroconversion and peaked around 35 months postseroconversion. In all patients, CrNA coincided with neutralizing activity against autologous viruses that were isolated <12 months postseroconversion, while viruses from later time points had already escaped autologous neutralizing activity. Also, the peak in gp160 sequence diversity coincided with the peak of CrNA titers. Individuals who lacked CrNA had lower peak autologous neutralizing titers, viral escape, and sequence diversity than individuals with CrNA. A better understanding of the underlying factors that determine the presence of CrNA or even an elite neutralizer phenotype may aid in the design of an HIV-1 vaccine.

Rapid development of glycan-specific, broad, and potent anti-HIV-1 gp120 neutralizing antibodies in an R5 SIV/HIV chimeric virus infected macaque

It is widely believed that the induction of a broadly neutralizing antibody (bNAb) response will be a critical component of a successful vaccine against HIV. A significant fraction of HIV-infected individuals mount bNAb responses, providing support for the notion that such responses could be elicited through vaccination. Infection of macaques with simian immunodeficiency virus (SIV) or SIV/HIV chimeric virus (SHIV) has been widely used to model aspects of HIV infection, but to date, only limited bNAb responses have been described. Here, we screened plasma from 14 R5-tropic SHIV-infected macaques for broadly neutralizing activity and identified a macaque with highly potent cross-clade plasma NAb response. Longitudinal studies showed that the development of broad and autologous NAb responses occurred coincidentally in this animal. Serum-mapping studies, using pseudovirus point mutants and antigen adsorption assays, indicated that the plasma bNAbs are specific for epitopes that include carbohydrates and are critically dependent on the glycan at position 332 of Env gp120. The results described herein provide insight into the development and evolution of a broad response, suggest that certain bNAb specificities may be more rapidly induced by immunization than others, and provide a potential model for the facile study of the development of bNAb responses.

Binding interactions between soluble HIV envelope glycoproteins and quaternary-structure-specific monoclonal antibodies PG9 and PG16

PG9 and PG16 are antibodies isolated from a subject infected with HIV-1 and display broad anti-HIV neutralizing activities. They recognize overlapping epitopes, which are preferentially expressed on the membrane-anchored trimeric form of the HIV envelope glycoprotein (Env). PG9 and PG16 were reported not to bind to soluble mimetics of Env. The engineering of soluble Env proteins on which the PG9 and PG16 epitopes are optimally exposed will support efforts to elicit broad anti-HIV neutralizing antibodies by immunization. Here, we identified several soluble gp140 Env proteins that are recognized by PG9 and PG16, and we investigated the molecular details of those binding interactions. The IgG versions of PG9 and PG16 recognize the soluble trimeric gp140 form less efficiently than the corresponding monomeric gp140 form. In contrast, the Fab versions of PG9 and PG16 recognized the monomeric and trimeric gp140 forms with identical binding kinetics and with binding affinities similar to the high binding affinity of the anti-V3 antibody 447D to its epitope. Our data also indicate that, depending on the Env backbone, the interactions of PG9 and PG16 with gp140 may be facilitated by the presence of the gp41 ectodomain and are independent of the proper enzymatic cleavage of gp140 into gp120 and gp41. The identification of soluble Env proteins that express the PG9 and PG16 epitopes and the detailed characterization of the molecular interactions between these two antibodies and their ligands provide important and novel information that will assist in improving the engineering of future Env immunogens.

Antibody responses against xenotropic murine leukemia virus-related virus envelope in a murine model

BACKGROUND

Xenotropic murine leukemia virus-related virus (XMRV) was recently discovered to be the first human gammaretrovirus that is associated with chronic fatigue syndrome and prostate cancer (PC). Although a mechanism for XMRV carcinogenesis is yet to be established, this virus belongs to the family of gammaretroviruses well known for their ability to induce cancer in the infected hosts. Since its original identification XMRV has been detected in several independent investigations; however, at this time significant controversy remains regarding reports of XMRV detection/prevalence in other cohorts and cell type/tissue distribution. The potential risk of human infection, coupled with the lack of knowledge about the basic biology of XMRV, warrants further research, including investigation of adaptive immune responses. To study immunogenicity in vivo, we vaccinated mice with a combination of recombinant vectors expressing codon-optimized sequences of XMRV gag and env genes and virus-like particles (VLP) that had the size and morphology of live infectious XMRV.

RESULTS

Immunization elicited Env-specific binding and neutralizing antibodies (NAb) against XMRV in mice. The peak titers for ELISA-binding antibodies and NAb were 1:1024 and 1:464, respectively; however, high ELISA-binding and NAb titers were not sustained and persisted for less than three weeks after immunizations.

CONCLUSIONS

Vaccine-induced XMRV Env antibody titers were transiently high, but their duration was short. The relatively rapid diminution in antibody levels may in part explain the differing prevalences reported for XMRV in various prostate cancer and chronic fatigue syndrome cohorts. The low level of immunogenicity observed in the present study may be characteristic of a natural XMRV infection in humans.

Characteristics of the earliest cross-neutralizing antibody response to HIV-1

Recent cross-sectional analyses of HIV-1+ plasmas have indicated that broadly cross-reactive neutralizing antibody responses are developed by 10%-30% of HIV-1+ subjects. The timing of the initial development of such anti-viral responses is unknown. It is also unknown whether the emergence of these responses coincides with the appearance of antibody specificities to a single or multiple regions of the viral envelope glycoprotein (Env). Here we analyzed the cross-neutralizing antibody responses in longitudinal plasmas collected soon after and up to seven years after HIV-1 infection. We find that anti-HIV-1 cross-neutralizing antibody responses first become evident on average at 2.5 years and, in rare cases, as early as 1 year following infection. If cross-neutralizing antibody responses do not develop during the first 2-3 years of infection, they most likely will not do so subsequently. Our results indicate a potential link between the development of cross-neutralizing antibody responses and specific activation markers on T cells, and with plasma viremia levels. The earliest cross-neutralizing antibody response targets a limited number of Env regions, primarily the CD4-binding site and epitopes that are not present on monomeric Env, but on the virion-associated trimeric Env form. In contrast, the neutralizing activities of plasmas from subjects that did not develop cross-neutralizing antibody responses target epitopes on monomeric gp120 other than the CD4-BS. Our study provides information that is not only relevant to better understanding the interaction of the human immune system with HIV but may guide the development of effective immunization protocols. Since antibodies to complex epitopes that are present on the virion-associated envelope spike appear to be key components of earliest cross-neutralizing activities of HIV-1+ plasmas, then emphasis should be made to elicit similar antibodies by vaccination.

Role of humoral immunity in host defense against HIV

Individuals infected with HIV-1 and nearly everyone vaccinated with HIV-1 vaccines will, in time, generate antibodies against viral proteins. These antibodies do not resolve natural infection, and vaccine candidates that successfully stimulate the production of high titers of neutralizing antibodies have failed to protect against infection. In spite of this, antibodies continue to be a focus of vaccine research. One reason for the continued interest in antibodies is the failure of a vaccine engineered to generate cell-mediated immunity against HIV. Successful protective immunity against most intracellular pathogens involves several arms of the immune response. A successful vaccine should also stimulate both protective cell-mediated immunity and specific antibody. Efforts should be directed toward making a vaccine that will stimulate the production of 1) more antibody, 2) more broadly cross-reactive neutralizing antibody (broadly neutralizing antibodies), and 3) antibody with a particular functional activity (antibody-dependent cell-mediated cytotoxicity; catalytic antibodies).

Rapid escape from preserved cross-reactive neutralizing humoral immunity without loss of viral fitness in HIV-1-infected progressors and long-term nonprogressors

A substantial proportion of human immunodeficiency virus type 1 (HIV-1)-infected individuals has cross-reactive neutralizing activity in serum, with a similar prevalence in progressors and long-term nonprogressors (LTNP). We studied whether disease progression in the face of cross-reactive neutralizing serum activity is due to fading neutralizing humoral immunity over time or to viral escape. In three LTNP and three progressors, high-titer cross-reactive HIV-1-specific neutralizing activity in serum against a multiclade pseudovirus panel was preserved during the entire clinical course of infection, even after AIDS diagnosis in progressors. However, while early HIV-1 variants from all six individuals could be neutralized by autologous serum, the autologous neutralizing activity declined during chronic infection. This could be attributed to viral escape and the apparent inability of the host to elicit neutralizing antibodies to the newly emerging viral escape variants. Escape from autologous neutralizing activity was not associated with a reduction in the viral replication rate in vitro. Escape from autologous serum with cross-reactive neutralizing activity coincided with an increase in the length of the variable loops and in the number of potential N-linked glycosylation sites in the viral envelope. Positive selection pressure was observed in the variable regions in envelope, suggesting that, at least in these individuals, these regions are targeted by humoral immunity with cross-reactive potential. Our results may imply that the ability of HIV-1 to rapidly escape cross-reactive autologous neutralizing antibody responses without the loss of viral fitness is the underlying explanation for the absent effect of potent cross-reactive neutralizing humoral immunity on the clinical course of infection.

Emergence of monoclonal antibody b12-resistant human immunodeficiency virus type 1 variants during natural infection in the absence of humoral or cellular immune pressure

Human immunodeficiency virus type 1 (HIV-1) resistance to broadly neutralizing antibodies such as b12, which targets the highly conserved CD4-binding site, raises a significant hurdle for the development of a neutralizing antibody-based vaccine. Here, 15 individuals were studied of whom seven developed b12-resistant viruses late in infection. The study investigated whether immune pressure may be involved in the selection of these viruses in vivo. Although four out of seven patients showed HIV-1-specific broadly neutralizing activity in serum, none of these patients had CD4-binding site-directed antibodies, indicating that strong humoral immunity is not a prerequisite for the outgrowth of b12-resistant viruses. In virus variants from one patient, who showed extremely weak heterologous and autologous neutralizing activity in serum, mutations were identified in the envelope that coincided with changes in b12 neutralization sensitivity. Lack of cytotoxic T-cell activity against epitopes with and without these mutations excluded a role for host cellular immunity in the selection of b12-resistant mutant viruses in this patient. However, b12 resistance correlated well with increased virus replication kinetics, indicating that selection for enhanced infectivity, possibly driven by the low availability of target cells in the later stages of disease, may coincide with increased resistance to CD4-binding site-directed agents, such as b12. These results showed that b12-resistant HIV-1 variants can emerge during the course of natural infection in the absence of both humoral and cellular immune pressure, suggestive of other mechanisms playing a role in the selective outgrowth of b12-resistant viruses.

High prevalence of neutralizing activity against multiple unrelated human immunodeficiency virus type 1 (HIV-1) subtype B variants in sera from HIV-1 subtype B-infected individuals: evidence for subtype-specific rather than strain-specific neutralizing activity

It is assumed that an effective human immunodeficiency virus type 1 (HIV-1) vaccine should be capable of eliciting neutralizing antibodies. However, even the best antibodies known to date lack neutralizing ability against a significant proportion of primary HIV-1 variants and, despite great efforts, still no immunogen is available that can elicit humoral immunity which is protective against infection or disease progression. We tested sera from 35 participants in the Amsterdam Cohort Studies on HIV-1 infection, who were all infected with HIV-1 subtype B and therapy-naïve at the time of sampling, for neutralizing activity against a panel of 23 tier 2-3 HIV-1 variants, with a minimum of five HIV-1 variants per subtype (A, B, C and D). Strong cross-clade neutralizing activity was detected in sera from seven individuals. Strikingly, sera from 22 of 35 individuals (63%) neutralized three or more of the six tier 2-3 HIV-1 subtype B viruses in the panel. There was a strong correlation between neutralization titre and breadth in serum. Indeed, the IC(50) of sera with strong cross-clade neutralizing activity was significantly higher than the IC(50) of sera with cross-subtype B activity, which, in turn, had a higher IC(50) than sera with the lowest neutralization breadth. These results imply that humoral immunity, at least in HIV-1 subtype B-infected individuals, is often subtype-specific rather than strain-specific and that the breadth of neutralization is correlated with the titre of neutralizing activity in serum. Considering the difficulties in designing a vaccine that is capable of eliciting cross-clade neutralizing activity, subtype-specific vaccines may be explored as an interesting alternative.